The growth plate cartilage is a specialized cartilagineous tissue responsible for the linear growth of the skeleton and some fracture repair. Alterations in endochondral growth plate ossification occurs in various crippling genetic diseases of cartilage and in common degenerative diseases such as osteoarthritis. The function of many genes coding for components of the extracellular matrix (ECM) expressed in the growth plate cartilage is not known. The goal of this proposal is to understand at the molecular level the regulation of expression and the function of Matrix gla protein (MGP) a mineral binding protein of the ECM of growth plate cartilage whose function is unknown. The mouse gene coding has been cloned. Study of its pattern of expression during development shows that MGP gene is expressed first in the zone of mesenchymal condensation that will generate cartilage and, at a later time in development, in the growth plate cartilage near the mineralization front. We propose 1). to perform a systematic analysis of MGP pattern of expression, at the mRNA and the protein level, during development and in post-natal life. The results of these morphological studies will be of critical importance to understand the possible phenotype of the transgenic mice we will generate. 2). We will use embryonic stem (E.S.) cell clones in which one allele of MGP gene has been disrupted to generate chimeric and eventually homozygous MGP deficient mice. These mice will be used as a tool to understand the function of this protein during the development of mammalian skeleton. 3). We plan also to study the transcriptional mechanisms governing the chondrocyte specific pattern of expression of MGP during development. We believe that the characterization of the function and of the regulation of expression of genes of the cartilagineous ECM such as MGP will increase understanding of the genetic pathways controlling chondrogenesis and may generate animal models for osteoarticular diseases.